Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium Alloy to Aluminum Alloy
A new welding method: ultrasonic assisted friction stir spot welding (UAFSSW) was put forward in the present study. UAFSSW was successfully applied to weld dissimilar AZ31 Mg alloy and 6061 Al alloy. Results show that for either conventional FSSW or UAFSSW, sound joints are obtained in the configura...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2016
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| Цитувати: | Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium Alloy to Aluminum Alloy / S.D. Ji, Z.W. Li, L. Ma, Y.M. Yue, S.S. Gao // Проблемы прочности. — 2016. — № 1. — С. 7-12. — Бібліогр.: 18 назв. — англ. |
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irk-123456789-1734122020-12-04T01:26:24Z Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium Alloy to Aluminum Alloy Ji, S.D. Li, Z.W. Ma, L. Yue, Y.M. Gao, S.S. Научно-технический раздел A new welding method: ultrasonic assisted friction stir spot welding (UAFSSW) was put forward in the present study. UAFSSW was successfully applied to weld dissimilar AZ31 Mg alloy and 6061 Al alloy. Results show that for either conventional FSSW or UAFSSW, sound joints are obtained in the configuration of upper Mg alloy and lower Al alloy. Ultrasonic vibration is beneficial to the upward flow of lower aluminum alloy, the increase of the stir zone (SZ) width and the refinement of the grains in the SZ. All cross sections of the Al–Mg joints exhibit the formation of intermetallic compounds (IMC) in the SZ. The crack of the conventional FSSW joint propagates exactly along the interface between the dissimilar materials and presents an inverted “V” morphology. After reaching the highest point of the hook defect, crack of the UAFSSW joint extends to the keyhole, leaving a portion of Mg alloy on the lower sheet. Conventional FSSW joint and UAFSSW joint show different IMC compositions at the faying interface. 2016 Article Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium Alloy to Aluminum Alloy / S.D. Ji, Z.W. Li, L. Ma, Y.M. Yue, S.S. Gao // Проблемы прочности. — 2016. — № 1. — С. 7-12. — Бібліогр.: 18 назв. — англ. 0556-171X http://dspace.nbuv.gov.ua/handle/123456789/173412 539.4 en Проблемы прочности Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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Научно-технический раздел Научно-технический раздел |
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Научно-технический раздел Научно-технический раздел Ji, S.D. Li, Z.W. Ma, L. Yue, Y.M. Gao, S.S. Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium Alloy to Aluminum Alloy Проблемы прочности |
| description |
A new welding method: ultrasonic assisted friction stir spot welding (UAFSSW) was put forward in the present study. UAFSSW was successfully applied to weld dissimilar AZ31 Mg alloy and 6061 Al alloy. Results show that for either conventional FSSW or UAFSSW, sound joints are obtained in the configuration of upper Mg alloy and lower Al alloy. Ultrasonic vibration is beneficial to the upward flow of lower aluminum alloy, the increase of the stir zone (SZ) width and the refinement of the grains in the SZ. All cross sections of the Al–Mg joints exhibit the formation of intermetallic compounds (IMC) in the SZ. The crack of the conventional FSSW joint propagates exactly along the interface between the dissimilar materials and presents an inverted “V” morphology. After reaching the highest point of the hook defect, crack of the UAFSSW joint extends to the keyhole, leaving a portion of Mg alloy on the lower sheet. Conventional FSSW joint and UAFSSW joint show different IMC compositions at the faying interface. |
| format |
Article |
| author |
Ji, S.D. Li, Z.W. Ma, L. Yue, Y.M. Gao, S.S. |
| author_facet |
Ji, S.D. Li, Z.W. Ma, L. Yue, Y.M. Gao, S.S. |
| author_sort |
Ji, S.D. |
| title |
Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium Alloy to Aluminum Alloy |
| title_short |
Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium Alloy to Aluminum Alloy |
| title_full |
Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium Alloy to Aluminum Alloy |
| title_fullStr |
Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium Alloy to Aluminum Alloy |
| title_full_unstemmed |
Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium Alloy to Aluminum Alloy |
| title_sort |
investigation of ultrasonic assisted friction stir spot welding of magnesium alloy to aluminum alloy |
| publisher |
Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| publishDate |
2016 |
| topic_facet |
Научно-технический раздел |
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http://dspace.nbuv.gov.ua/handle/123456789/173412 |
| citation_txt |
Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium Alloy to Aluminum Alloy / S.D. Ji, Z.W. Li, L. Ma, Y.M. Yue, S.S. Gao // Проблемы прочности. — 2016. — № 1. — С. 7-12. — Бібліогр.: 18 назв. — англ. |
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Проблемы прочности |
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2025-07-15T10:04:09Z |
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| fulltext |
SCIENTIFIC AND TECHNICAL
SECTION
UDC 539.4
Investigation of Ultrasonic Assisted Friction Stir Spot Welding of Magnesium
Alloy to Aluminum Alloy
S. D. Ji,
1
Z. W. Li, L. Ma, Y. M. Yue, and S. S. Gao
Faculty of Aerospace Engineering, Shenyang Aerospace University, Daoyi Development District,
Shenyang, China
1 superjsd@163.com
A new welding method: ultrasonic assisted friction stir spot welding (UAFSSW) was put forward in
the present study. UAFSSW was successfully applied to weld dissimilar AZ31 Mg alloy and 6061 Al
alloy. Results show that for either conventional FSSW or UAFSSW, sound joints are obtained in the
configuration of upper Mg alloy and lower Al alloy. Ultrasonic vibration is beneficial to the upward
flow of lower aluminum alloy, the increase of the stir zone (SZ) width and the refinement of the grains
in the SZ. All cross sections of the Al–Mg joints exhibit the formation of intermetallic compounds
(IMC) in the SZ. The crack of the conventional FSSW joint propagates exactly along the interface
between the dissimilar materials and presents an inverted “V” morphology. After reaching the
highest point of the hook defect, crack of the UAFSSW joint extends to the keyhole, leaving a portion
of Mg alloy on the lower sheet. Conventional FSSW joint and UAFSSW joint show different IMC
compositions at the faying interface.
Keywords: ultrasonic assisted friction stir spot welding, intermetallic compounds, magnesium
alloy, aluminum alloy, fracture position.
Introduction. In the last few decades, as the resource shortage and environment
protection problems become severer, weight-saving structures have become a hotspot in
industries of aerospace and transportations. Therefore, light materials are being extensively
used now [1–3]. As a new variant of friction stir welding (FSW), friction stir spot welding
(FSSW) owns advantage of lower energy consumption, smaller distortion, less welding
defects and higher joint quality compared to resistance spot welding (RSW) [4]. Being a
solid state joining technology, FSSW is more suitable to weld light materials such as
aluminum alloys and magnesium alloys [5–8].
Since the invention of FSSW, many investigations about FSSW joints of Al alloy or
Mg alloy have been reported [9–15]. Yin et al. [9] performed FSSW on AZ31 aluminum
alloy and reported that better failure loads can be attained under conditions of larger
bonded width, outward curved hook and smaller hook height. Bozzi et al. [10] found out
that the FSSW joint strength was largely determined by the stir zone (SZ) width and the
hook defect. Besides, some investigations about FSSW dissimilar Al and Mg alloys have
been published. Rao et al. [13] investigated effects of the tool rotating speed on dissimilar
AM60B Mg alloy and 6022-T4 Al alloy FSSW joints and studied the intermetallic
compounds (IMCs) in the SZ. Furthermore, Sato et al. [15] studied the interfacial
microstructure on the lap shear strength of Al alloy to Mg alloy FSSW joint. Lots of
important conclusions can be obtained from these studies. However, before successful
application of the Al–Mg FSSW joints, plenty of researches need to be done.
© S. D. JI, Z. W. LI, L. MA, Y. M. YUE, S. S. GAO, 2016
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2016, ¹ 1 7
Ultrasonic assisted FSW (UAFSW) is a new derivative process of FSW. The
ultrasonic vibration can increase the heat input during the welding process and decreases
the welding force [16]. In the last few years some researches about UAFSW or ultrasonic
assisted FSSW (UAFSSW) have been done [16–18]. Rostamiyan et al. [16] investigated the
microstructure and mechanical properties of 6061 aluminum alloy conventional FSSW and
UAFSSW joints. Liu et al. [17] and Shi et al. [18] reported the material flow behavior of
UAFSW and discovered that the material flow behavior was evidently enhanced during
UAFSW. However, studies about UAFSSW of magnesium to aluminum alloys have not
been reported yet. Therefore, in the present study, UAFSSW was applied to weld Mg alloy
and Al alloy. Effects of ultrasonic vibration on hook defect, SZ width, microstructure of the
joints, distribution of the IMC and fracture paths were studied in detail.
Experiment Process. AZ31B magnesium alloy and 6061-T6 aluminum alloy were
used as the base material (BM) in the present study. Dimensions and configuration of the
two sheets are indicated in Fig. 1. Prior to welding, all sheets were cleaned with sand paper
to clean off the oxidation layer. The rotating tool was composed of a concentric shoulder
and a tapered pin. The diameter of the shoulder is 11 mm and the pin has a right-hand
threaded. Diameters of the pin root and bottom are 5 to 3 mm, respectively. The
FSW-3LM-4012 machine was used in the experiment. The tool rotated in an anti-clockwise
direction and the tilted angle is 0�. Ultrasonic vibration was exerted 5 s before the plunge of
the pin and it was exerted on the lower plate under the SZ, as shown in Fig. 1. The
vibration frequency was 19 kHz. Pin rotating speed and dwell time were 1000 rpm and 5 s.
Other parameters such as plunge speed, shoulder plunge depth, and retracting speed are 5
mm/min, 0.3 mm, and 10 mm/min, respectively. After the refraction of the pin, the
ultrasonic vibration lasted for another 5 s.
After welding, the metallographic specimens were cut through the center of the joint
using a wire electrical discharge cutting machine. Then the specimens were burnished,
polished and etched with Keller’s reagent. Metallographic analysis was carried out using an
optical microscopy (OLYMPUS-G71). Fracture positions of the specimens were observed
using a stereoscopic microscope (ZSA403). The IMC composition was examined using a
SU3500 scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy
(EDX) capabilities.
Results and Discussion. Cross sections of conventional FSSW and UAFSSW joints
are shown in Fig. 2. It can be seen that in the SZ, 6061 Al alloy flows upwards and mixes
with the AZ31 alloy due to the rotation of the tool. An up-bending interface exists between
the AZ31 Mg alloy and the 6061 Al alloy, which is called the hook defect. According to
Yin et al. [9], the geometry of the hook defect largely influenced the lap shear failure of the
joint and better mechanical properties were attained when the hook height was small. As
shown in Fig. 2a, 6061 Al alloy not only flows upwards into the upper sheet but also flows
outwards. Hence, hook defect of the conventional FSSW joints curved outwards from the
axis of the rotating pin. In the UAFSSW joints in Fig. 2b, 6061 Al of the lower sheet
mainly shows upward flow and the hook defect is flatter.
S. D. Ji, Z. W. Li, L. Ma, et al.
8 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2016, ¹ 1
Fig. 1. A schematic illusion of the ultrasonic vibration during welding.
The SZ width refers to the width from the origin of the hook defect to the keyhole. As
shown in Fig. 2, SZ width is 1.34 mm of conventional FSSW joint while this width of the
UAFSSW joint is 1.65 mm. The maximum flow distance of Al alloy on the conventional
FSSW and UAFSSW tool is 1.13 and 1.29 mm, respectively. The results agree with the
conclusion of Shi et al. [18]. During the UAFSSW process, the material flow behavior of
the SZ is enhanced due to the ultrasonic vibration, which means more material adjacent the
original SZ will be driven to flow. Therefore, the enhanced material flow behavior is
beneficial to the upward flow of the lower 6061 Al alloy, as shown in Fig. 2b.
As shown in Fig. 3, at the end section of the hook defect, mixing degrees between the
two materials show much difference. On conventional FSSW joint, mixing degree between
6061 Al and AZ31 Mg is not so adequate and the intersection where IMC always appear
can be clearly recognized. Better mixing is formed on UAFSSW joint. As shown in Fig. 3b,
plenty of complex lamellar-like shear bands formed between 6061 Al alloy and AZ31 Mg
alloy. Therefore, the conclusion can be attained that ultrasonic vibration can enhance
material mixing when welding dissimilar alloys.
In FSW, the microstructure of the SZ plays a predominant part on joints quality. In
general, uniform and fine grains of the SZ always results in better strength and higher
hardness. On the contrary, non-uniform grains of the SZ leads to poor joint strength. The
grains of the SZ on the conventional FSSW joint and UAFSSW joint are shown in Fig. 4. It
can be seen that compared with grains shown in Fig. 4a, uniform and refiner grains are
observed on the UAFSSW joint. During the UAFSSW process, the fluidity of material is
evidently enhanced due to the ultrasonic vibration. Higher flow velocity is beneficial for
the strain and strain rate of the material in SZ, which is beneficial to the dynamic
Investigation of Ultrasonic Assisted Friction Stir Spot Welding ...
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2016, ¹ 1 9
Fig. 2. Cross sections of the FSSW joints: (a) conventional FSSW joint; (b) UAFSSW joint; (c)
magnified view of the region marked (a); (d) magnified view of the region marked (b).
Fig. 3. Mixing of the dissimilar materials on two different joints: (a) conventional FSSW joint; (b)
UAFSSW joint.
recrystallization. Therefore, finer grains are attained in the SZ of the UAFSSW joint. As
shown in Fig. 4, the average size of the grains decreases from 8 to 4 �m when the
UAFSSW is used.
Fracture positions of the conventional FSSW joints and UAFSSW joints are shown in
Fig. 5. It can be seen that both joint fracture at the hook defect firstly. When it comes to the
region adjacent to the keyhole, crack propagation path shows difference. As shown in
Fig. 5a, in conventional FSSW joint, crack propagates exactly along the interface between
the two materials and presents an inverted “V” shape. On the UAFSSW joint, after
initiating at the tip of the hook, the crack propagates along the hook and then upwards. At
the region adjacent to the keyhole, crack shows a flat fracture path towards the keyhole
instead of exactly along the interface. A portion of Mg alloy remains at the lower Al alloy,
as shown in Fig. 5e and 5f.
Figures 6 and 7 show the SEM images and the EDX analysis results of the region E,
F, and G marked in Fig. 5. As shown in Fig. 6a, the main component of the IMC is
47.329% Mg and 51.246% Al at the Mg side. While at the Al side, the IMCs are mainly
composed of 32.037% Mg and 64.637% Al. Therefore, it is believed that on the lap
interface of conventional FSSW joints, the Al3Mg2 is the main component of the IMC. As
shown in Fig. 7, region B locates at the interface between the two dissimilar alloys. The
main components of the IMC are 53.464% Mg and 43.484% Al. It can be seen the
percentage of the Mg is much bigger than that on the conventional FSSW joint. Possible
reason for this is that when the ultrasonic vibration was used, material flow behavior at the
lap interface was evidently enhanced. The mixing degree between the two materials
becomes better on the UAFSSW joint, leading to an average elemental composition. It is
believed on the UAFSSW joints, Al12Mg17 is the main component of the IMC.
10 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2016, ¹ 1
Fig. 4. Grains in the SZ on two different joints: (a) conventional FSSW joint; (b) UAFSSW joint.
Fig. 5. Fracture positions of the joints: (a) general view of the conventional FSSW joint; (b) magnified
view of the region A; (c) magnified view of the region B; (d) general view of the UAFSSW joint;
(e) magnified view of the region C; (f) magnified view of the region D.
S. D. Ji, Z. W. Li, L. Ma, et al.
Conclusions. In the present study, UAFSSW was used to weld dissimilar Mg alloy
and Al alloy, effects of ultrasonic vibration on the material flow, mixing degree, SZ grains
and fracture modes of the conventional FSSW and UAFSSW joints were studied. The
following conclusions can be drawn:
1. Ultrasonic vibration is beneficial for the upward flow of the lower sheet material.
The upward flow distance and width of SZ on the UAFSSW joint are much bigger than
those on the conventional FSSW joint. The mixing degree of the dissimilar materials is
much better when ultrasonic vibration is used.
2. The grain size of the SZ on the UAFSSW joint is smaller than that on the
conventional FSSW joint because of the ultrasonic vibration.
3. On the conventional FSSW joint, crack exactly propagates along the faying
interface of dissimilar materials. On the UAFSSW joint at the region adjacent to the
keyhole, crack shows a flat fracture path towards the keyhole instead of exactly along the
interface, leaving a portion of Mg alloy at the lower Al alloy.
4. The main component of the IMC at the lap interface on the conventional FSSW
joint is Al3Mg2 and the main component of the IMC at the lap interface on the UAFSSW
joint is Al12Mg17.
Acknowledgments. This work is supported by the National Natural Science Foundation
of China (No. 51204111), the Education Department Foundation of Liaoning Province
(Nos. LJQ2012015 and L2012047), the Natural Science Foundation of Liaoning Province
(No. 2013024004) and the Project of Science and Technology Department of Liaoning
Province (No. 2013222007).
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ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2016, ¹ 1 11
Fig. 6. EDX results on the conventional FSSW joint: (a) region E; (b) region F.
Fig. 7. EDX results of region G on the UAFSSW joint.
Investigation of Ultrasonic Assisted Friction Stir Spot Welding ...
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Received 03. 08. 2015
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